NPT- National Pipe Thread Taper- ANSI B1.20.1

NPT pipe threads - dimensions according ANSI/ASME B1.20.1

Common American National Standard Pipe Taper Threads

  • NPT - National Pipe Thread Taper
  • NPTF - Dryseal American National Standard Taper Pipe Thread (ANSI B1.20.3)

NPT threads may be referred to as MPT ('Male Pipe Thread'), MNPT, or NPT(M) for male (external) threads, and FPT ('Female Pipe Thread'), FNPT, or NPT(F) for female (internal) threads. Note that FPT and MPT are not authorized designations per the ANSI standard.

For NPT threads a sealant compound or Teflon tape must be used for a leak-free seal. For NPTF no sealant is needed for a leak tight connection.

Characteristics of NPT (also known as ANSI/ASME B1.20.1 Pipe Threads, General Purpose):

  • the angle between the taper and the center axis of the pipe is  1o 47' 24'' (1.7899o)
  • truncation of roots and crests are flat
  • 60o thread angle
  • pitch is measured in threads per inch

Note! Pipe sizes do not refer to any physical dimensions. The outside diameter of a pipe or fitting must be measured and compared to a table for size identification. A 3/4" NPT pipe thread has an outside diameter - OD - of 1.050 inches.

Each thread size has a defined number of threads per inch - TPI, or pitch. The 3/4" NPT pipe thread has 14 threads per inch. Both the TPI and OD of the thread are required for positive identification of thread size because more than one size have the same TPI.

NPT - American Standard Pipe Thread Taper 1)
Pipe Size
(inches)
Threads per Inch
TPI - pitch
Approximate Length of Thread (inches) Approximate Number of Threads to be Cut Approximate Total thread Makeup, Hand and Wrench (inches) Nominal Outside Pipe Diameter
OD
(inches)
Tap Drill
(inches)
1/16" 27 0.313  
1/8" 27 3/8 10 1/4 0.405 R
1/4" 18 5/8 11 3/8 0.540 7/16
3/8" 18 5/8 11 3/8 0.675 37/64
1/2" 14 3/4 10 7/16 0.840 23/32
3/4" 14 3/4 10 1/2 1.050 59/64
1" 11-1/2 7/8 10 9/16 1.315 1-5/32
1-1/4" 11-1/2 1 11 9/16 1.660 1-1/2
1-1/2" 11-1/2 1 11 9/16 1.900 1-47/64
2" 11-1/2 1 11 5/8 2.375 2-7/32
2-1/2" 8 1 1/2 12 7/8 2.875 2-5/8
3" 8 1 1/2 12 1 3.500 3-1/4
3-1/2" 8 1 5/8 13 1 1/16 4.000 3-3/4
4" 8 1 5/8 13 1 1/16 4.500 4-1/4
4 1/2" 8 5.000 4-3/4
5" 8 1 3/4 14 1 3/16 5.563 5-9/32
6" 8 1 3/4 14 1 3/16 6.625 6-11/32
8" 8 1 7/8 15 1 5/16 8.625  
10" 8 2 16 1 1/2 10.750  
12" 8 2 1/8 17 1 5/8 12.750  
14" 8 14.000  
16" 8 16.000  

1) The taper rate is 1 in 16 inch (3/4 inch in a foot or 62.5 mm in a meter)

NPT threads are not interchangeable with NPS - National Pipe Straight - threads.

NPT threads may look similar to ISO 7/1 threads. However, ISO and NPT threads should not be mixed. ISO threads have 55o taper angle versus 60o for NPT. The NPT root and crest configurations are also different from ISO. For ISO threads pitch is usually measured in millimeters (may be expressed in Inch). The pitch are different.

Related Topics

  • Dimensions - Sizes and dimensions of pipes and tubes, and their fittings - inside and outside diameter, weight and more

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